The immunological mechanisms to reject foreign material are generally comprised of: the humoral immunity which involves macrophages that recognize antigens and function as antigen presenting cells, helper T cells that activate other T cells etc. by recognizing antigen presented by said macrophages and then producing various cytokines, B cells that differentiates into antibody-producing cells by the action of said lymphokines etc., as well as the cellular immunity in which killer T cells that undergo differentiation in response to antigen presentation, and attack and destroy the target cells.
At present, cancer immunity is mainly considered to be derived from cellular immunity in which killer T cells participate. In the killer T cell-involved cancer immunity, precursor T cells that recognized tumor antigen presented in the form of a complex between the major histocompatibility complex (MHC) class I and the tumor antigen differentiate and propagate to produce killer T cells, which attack and destroy tumor cells. At this time, tumor cells present, on the surface thereof, the complex of the MHC class I antigen and the tumor antigen, which is targeted by the killer T cells (Cur. Opin. Immunol., 5: 709, 1993; Cur. Opin, Immunol, 5: 719, 1993; Cell, 82: 13, 1995; Immunol. Rev., 146: 167, 1995).
The above tumor antigen presented by the MHC class I antigen on the surface of the target tumor cells is considered to be a peptide composed of about 8 to 12 amino acids produced after the antigen protein synthesized in the tumor cells underwent processing by intracellular proteases (Cur. Opin. Immunol., 5: 709, 1993; Cur. Opin, Immunol, 5: 719, 1993; Cell, 82: 13, 1995; Immunol. Rev., 146: 167, 1995).
Currently, antigen proteins are being searched for various cancers, but few have been demonstrated as cancer specific antigens.
WT1, a Wilms tumor suppressor gene (WT1 gene) was isolated from chromosome 11p13 as one of the causative genes of Wilms tumor based on the analysis of the WAGR syndrome that was complicated by Wilms tumor, aniridia, urogenital anomaly, mental retardation, etc. (Gessler, M. et al., Nature, 343: 774-778 (1990)), and the genomic DNA is about 50 Kb and is composed of ten exons, of which cDNA is about 3 kb. The amino acid sequence deduced from the cDNA is as set forth in SEQ ID NO: 1 (Mol. Cell. Biol., 11: 1707, 1991).
From the facts that the WT1 gene is highly expressed in human leukemia and that the treatment of leukemia cells with WT1 antisense oligomers results in suppression of cellular growth (Japanese Unexamined Patent Publication (Kokai) No. 9-104627), the WT1 gene has been suggested to promote the growth of leukemia cells. Furthermore, WT1 was found to be highly expressed in solid tumors such as gastric cancer, colon cancer, lung cancer, breast cancer, lung cell cancer, hepatic cancer, skin cancer, bladder cancer, prostate cancer, uterine cancer, cervical cancer, and ovarian cancer (Japanese Patent Application (Tokugan) 9-191635), and the WT1 gene was demonstrated to be a new tumor marker in leukemia and solid tumors. However, it has not been confirmed that the expression products of the WT1 gene are tumor-specific antigens useful as a cancer vaccine.